1. Field of the Invention
The present invention relates to a trimming capacitor and more particularly to a trimming capacitor which is adapted to being trimmed by a laser beam.
2. Description of the Prior Art
A trimming capacitor is used when an adjustable electrostatic capacitance that can take various values is required. For instance, as shown in FIG. 7, a trimming capacitor 50 has a wide trimming capacitor electrode 54 on the surface of a ceramic dielectric 51 containing internal capacitor electrodes 52 and 53. The reference numerals 60 and 61 in FIG. 7 denote external input and output electrodes. The electrostatic capacitance can be adjusted by reducing the area of the trimming capacitor electrode 54 facing the capacitor electrode 53, by removing a part 54a of the trimming capacitor electrode 54 with a laser beam L.
A dielectric ceramic material is generally used as the material of the ceramic dielectric 51. The dielectric ceramic material is normally sintered in air and is reduced readily within a neutral or reducing atmosphere.
However, because the dielectric ceramic material is used as the material of the ceramic dielectric 51 in the prior art trimming capacitor 50, there has been a problem that, when heated by the high energy of the laser beam L directed at the trimming capacitor electrode 54, a part 51a of the ceramic dielectric 51 is reduced and is turned into a semiconductor, thus dropping the Q of the capacitor.
Accordingly, there is a need to provide a trimming capacitor in which the drop in the Q during laser trimming can be reduced.